A Rock-on-a-Chip Approach to Study Fluid Invasion and Flowback in Liquids-Rich Shale Formations

Abstract Understanding the dynamic process of fluid invasion and flowback has significant technological implications in developing shale plays. One of the physical models used to study this process is coreflooding, which mimics the process of fracturing fluid invasion, flowback, and hydrocarbon recovery from shale formations. However, coreflooding is time consuming, expensive, and unable to provide insights to the underlying physics at the pore scale level in most instances. Rock-on-a Chip (ROC), based on microfluidic technology, is an emerging approach that provides a new method to study fracturing fluid invasion and flowback affected by the petrophysical properties using direct visualization and measurement. In this study, the porous matrix, representing shale formations, and single large channel, representing hydraulic fractures or natural fractures, were defined in an oil-wet microfluidic chip; the drainage-imbibition cycles that are analogous to fracturing fluid invasion and subsequent flowback were measured by optical microscopy. Specifically, the effect of interfacial tension and fracture patterns ("half" fracture and "S" fracture) on the fluid invasion factor and flowback efficiency was examined. The results show that the invasion factor and flowback efficiency correlated well with the capillary pressure of fracturing fluids. In addition, model fractures have a major effect on the flowback. In particular, the invasion factor and flowback efficiency of the water-based fracturing fluids were significantly impaired in the "S" fracture pattern, as compared to homogeneous and half fracture patterns. Notably, by improving fluid mobility between the porous matrix and fractures, the addition of a surfactant to the fracturing fluids significantly enhanced the fluid invasion and flowback in all of the fracture patterns. The results demonstrate that the ROC model proposed in this work can be used to study the flowback process affected by properties such as wettability, permeability, initial water saturation, and reservoir pressure. Consequently, it has potential for guiding water management and chemical treatment in hydraulic fracturing.